Pressurized ink jet printing systems require the supply of ink at relatively high pressures and relatively low flow rates. An example of a pressurized ink jet printing system is shown in Sweet et al, U.S. Pat No. 3,373,437 where pressurized electrically conductive fluid is ejected from a row of orifices for breaking into streams of uniform drops. As each drop breaks off from its fluid filament as ejected from the corresponding orifice, it may be selectively charged by an associated charge electrode. The charge electrodes are thus arranged in a row corresponding to and spaced from the row of orifices so that the fluid streams may pass therethrough. The drops then pass through an electrostatic deflection field and each drop is deflected a distance which is related to the magnitude of the drop charge. The drops may be charged binarily so that the uncharged drops are undeflected and continue past the deflection field to impact a recording medium for printing while the charged drops are deflected to a drop catcher or gutter.
The nozzles used in such an arrangement may, for example, be 8 mils in diameter. Thus, even though a hundred or more nozzles may be used, the total flow is still quite small. The customary devices used in such low flow rate situations are a relieving regulator or a relief valve. An example of such a system is illustrated in Helgeson et al U.S. Pat. No. 3,761,953 wherein a pressure tank has an inlet larger than the outlet causing the tank to fill so that the ink presses against a diaphragm or valve. Air at a regulated pressure is supplied to the opposite side of the diaphragm causing it to seal so long as the pressure of the ink within the vessel is below that of the pressure of the air. The input rate of the ink is greater than the output rate so that, at some point, the pressure of the ink within the vessel exceeds the pressure of the air in the cavity, opening the diaphragm or valve to relieve the pressure.
The difficulties with this or similar relief valve arrangements are that only the maximum pressure is regulated and that the pressure drop when the relief valve opens is relatively abrupt. This abruptness must then be compensated for by other controlled pressure regulators or by expansion chambers. The systems therefore become quite complex in order to be suitable for fluid handling systems having low flow rates, such as ink jet.